The present invention pertains to the an of liquid dispensers, and, more particularly, to a dispensing device for accurately dispensing small droplets of liquid. The invention is particularly applicable for use as an eyedropper and will be described with particular reference thereto although it will be appreciated that the invention has other and broader applications.
Medicament drop dispensers of the type to which the present invention pertains are available in various sizes and shapes for the numerous medicines and solutions which are available for the care and comfort of the human eye. Heretofore, such dispensers have basically comprised a relatively small compressible plastic container or vial provided with a dispensing nozzle and cap.
One problem associated with conventional eyedroppers is the difficulty in accurately controlling the amount of medicine dispensed, i.e., the number of drops dispensed. Most conventional eyedropper dispensers utilize one of two or a combination of these methods to achieve single drop control.
One method uses a highly compliant plastic bottle which the user squeezes to dispense a drop. The extensive deflection of the bottle creates a significant internal air pressure within the vial which expels the liquid through the tip or dispensing nozzle. In order to prevent a continuous stream of liquid medicament from being expelled, and to create single drops, these designs incorporate a flow restriction at the inlet of the tip or nozzle. Unfortunately, this flow restriction does not s limit the number of drops expelled during a single squeeze, but merely limits the liquid medicament flow rate flavoring the formation of individual drops releasing from the dropper tip rather than a continuous stream. It should be obvious that this flow restriction, if truly effective in preventing a stream of liquid, will also make the dispensing of drops more difficult, especially for older patients as well as those with physical disabilities. Also, the creation of a very small molded orifice, frequently as small as 0.005" (0.13 mm) in diameter creates manufacturing difficulties. In addition, the small orifice can be prone to clogging from particles of contamination sometimes drawn back into the bottle during usage or dried residue from the medicament formulation itself.
Another method often used is to manufacture a bottle with relatively rigid (relatively non-compliant) walls. With this configuration, the force to deflect or squeeze the bottle is relatively high compared to the compliant bottle of the previous paragraph. Because of this increased force necessary to deflect the plastic walls of the bottle, the user will tend to limit the squeezing action due to the difficulty encountered in the movement. However, increased force on the bottle will easily create a stream of liquid medicament to be expelled rather than a drop. Another disadvantage of this design is that it is frequently difficult to dispense even a single drop, especially for older patients as well as those with physical disabilities.